The present invention relates to the general field of turbomachines having two contrarotating fans mounted at the front. The invention relates more particularly to a specific arrangement of a turbomachine with contrarotating fans suitable for facilitating the assembling and disassembling of the various bodies making it up.
In conventional turbomachines having a large bypass ratio, the fan section comprises a single row of large-diameter rotor blades. The peripheral speed at the tips of the blades is proportional to said diameter and to the speed of rotation of the fan. In order to obtain good efficiency, this peripheral speed must be below the speed of sound. This can be achieved by interposing stepdown gearing between the shaft for driving the blades and the fan. However such gearing increases the weight of the engine and the turbomachine often presents low efficiency together with high specific fuel consumption.
In order to increase efficiency and reduce specific fuel consumption, it is known to fit the fan section of a turbomachine with two rows of blades (i.e. two fans) that are axially spaced apart from each other, with each being driven directly by a low-pressure shaft without any interposed gearing. In that type of turbomachine, each fan contributes in practically identical manner to propulsion. Thus, U.S. Pat. No. 4,860,537 discloses a turbomachine that uses contrarotating turbine sections (i.e. sections turning in opposite directions) that drive likewise contrarotating fans.
Turbomachines with contrarotating fans known in the prior art present problems of assembling and disassembling the various elements that make them up. In particular, the operations of assembling and disassembling the shaft of the rear fan are made almost impossible by the specific disposition of systems for securing said rear fan shaft on the appropriate low-pressure drive shaft. Furthermore, it is also very difficult to feed cooling and lubricating oil to the bearings that are mounted between the front and rear fan shafts.